Conventionally, for example as disclosed in JP-2005-317751 corresponding to US 2005/0258493, a reverse conduction type semiconductor device (i.e., RC-IGBT or reverse conducting IGBT) includes an IGBT (insulated gate bipolar transistor) and a FWD (free wheel diode), which are disposed in the same semiconductor substrate, so that the FWD is built in the IGBT.
In the RC-IGBT, an anode electrode of the FWD and an emitter electrode of the IGBT are common, and a cathode electrode of the FWD and a collector electrode of the IGBT are common. The RC-IGBT is mounted in an inverter circuit so that the RC-IGBT executes PWM control of a load.
However, when the RC-IGBT is assembled in the inverter circuit, a driving signal to be input into the gate electrode of the IGBT is, in general, a phase reversal signal in an up-down arm direction. Thus, even when the FWD performs a free wheel function, the driving signal is input into the gate electrode of the IGBT. Accordingly, the FWD and the IGBT function at the same time.
When the FWD and the IGBT function at the same time, i.e., when the gate of the IGBT turns on at the time when the FWD functions, the electric potential of the anode is equalized with the electric potential of the cathode of the FWD since the above electrodes are common. Thus, the FWD hardly performs a forward function. Thus, when the driving signal is input into the gate electrode of the IGBT, a forward voltage Vf of the FWD increases, and thereby, a DC loss of the semiconductor device becomes large.
To avoid the above difficulty, a region of the IGBT and a region of the FWD are separated from each other. This device structure is disclosed in, for example, Proceedings of 2004 International Symposium on Power Semiconductor Devices & Ics, on page 261-264. The gate electrode of the IGBT is not arranged in the region of the FWD, so that the FWD as a body diode is not built in the IGBT. However, the region of the FWD, which provides diode function, and does not provide IGBT function, becomes wide. Accordingly, when a chip size of the device is the same, the region of the IGBT becomes narrow. That is, an occupancy rate of the region of the IGBT in the chip is reduced since the FWD single purpose region is arranged in the chip. In this case, an on-state voltage Von of the IGBT increases, and the DC loss of the semiconductor device increases. Further, when the on-state voltage Von of the IGBT is fixed to be small, the dimensions of the chip become large.